In pulp recycling operations, scrap paper is most often shredded and mixed with water, in devices known as primary pulpers. Some of these devices are shaped as a container, the bottom part of which is provided with a rotating stirrer-disintegrator member placed on top of a perforated grid. This grid gives passage to a pulp which is still in a crude and soiled condition and it thereafter sent on to a secondary sorting apparatus, such as the one described in U.S. Pat. No. 4,200,537 granted Apr. 29, 1980 (French Patent Pub. No. 2,410,081 Del. Oct. 11, 1982).
Oversize material accumulating on this grid will gradually cause a plugging of the grid, so that it will need to be cleared out. According to a recent technique, this refuse material is evacuated from the lower part of the grid and is then washed in a closed apparatus such as described in U.S. Pat. Nos. 4,369,093 granted Jan. 1, 1983, and 4,493,296 granted Apr. 17, 1984 (French Patent Pub. No. 2,411,681 Del. Jan. 17, 1983).
According to this technique and using this equipment, the recovered pulp is recycled to the primary pulper while the washed-out refuse material is discarded. In fact, the product being fed to this device from the primary pulper is not sufficiently disintegrated, while this device itself has a high disintegrating power, bringing about the need to pass the recovered pulp once more through the primary pulper.
Other types of equipment for the preparation of scrap paper, particularly those known as helix or "helico" pulpers, are not provided with a grid, and have no sorting action whatever, not even a crude one. They merely operate a disintegration, bringing the paper fibers to form a suspension in the presence of water without altering the contaminants which retain their dimensions and shape. These devices deliver a mixture containing approximately 15% to 20% dry material, which is then discharged into a large open vat where it is stirred by means of a stirrer, water being added until the dry material concentration drops to about 5%. The product is then pumped out by means of a special pump for being fed to a continuously operating separator of the screening trommel or vibrating sieve type. This sort of equipment requires a pump being capable of absorbing large pieces of contaminants, and a pump of this kind is subject to frequent breakdowns.
On another hand, devices such as screening trommels or vibrating screens have only a small throughput, so that the above mentioned pump must work with a small flow, which leads to the adoption of volumetric pumps. Such pumps are very costly and put a heavy strain on the installation costs.
This invention has the purpose of providing a method and apparatus for solving the above-mentioned drawbacks.